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Using implicit loop with -n
Topicalization and Special Variables example from a Well House Consultants training course
More on Topicalization and Special Variables [link]

This example is described in the following article(s):
   • Seven new intermediate Perl examples - [link]

Source code: spot Module: P210
#!/usr/bin/perl -n

=head1 Tiny code in Perl

The code above uses the -n option which implies
that it runs within a loop that reads each line
in turn from a file named on the command line
and stores it in the "default input and pattern
matching space" a.k.a. $_ ...

It's open to debate whether or not coding in this
way is good practise - my personal view is that
it's great for occasional utilities where you just
need to quickly filter a data file on one or two
occasions, but it's not a good idea for long term
coding where you need to have maintaiance in mind.



Sample output:

Dorothy:p82 grahamellis$ ./spot ../Downloads/access_log.xyz
o_whelk - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
sardine - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
mussel - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
skate - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
whale - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
trout - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
seal - - "GET /pub/graham/cliad.html HTTP/1.0" 200 323
Dorothy:p82 grahamellis$

Learn about this subject
This module and example are covered on the following public courses:
 * Perl Programming
 * Perl bootcamp
 * Learning to program in Perl
 * Perl Programming
Also available on on site courses for larger groups

Books covering this topic
Yes. We have over 700 books in our library. Books covering Perl are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "Topicalization and Special Variables" training module. You'll find a description of the topic and some other closely related examples on the "Topicalization and Special Variables" module index page.

Full description of the source code
The complete training module that describes this source code is availble for download (for limited use) from our download centre.

Other resources
• Our Solutions centre provides a number of longer technical articles.
• Our Opentalk forum archive provides a question and answer centre.
The Horse's mouth provides a daily tip or thought.
• Further resources are available via the resources centre.
• All of these resources can be searched through through our search engine
• And there's a global index here.

Purpose of this website
This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

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This web site is written and maintained by Well House Consultants.

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